Tractors equipped with dozing blades are used for a great many different purposes. Applications which will be familiar to most include pushing loose material such as landfill trash, construction debris, and soil about a worksite. Such dozing activities are indispensable to forestry, waste handling, building construction, and light to medium civil engineering. Small to mid-sized tractors are commonly used in these industries.
Dozing is also an integral part of larger scale activities such as mining and major civil engineering projects. In these contexts, rather than pushing loose material across a surface, tractors equipped with dozing blades are often used to dig material from a substrate. In the case of rocky terrain, commonly encountered in opencast mines, or where substrate materials otherwise have a high structural integrity, quite large and powerful machines equipped with rugged dozing blades are often required. These and analogous activities are generally referred to as “production dozing.” In production dozing, a tractor equipped with a heavy-duty dozing blade is typically driven across, and through, a substrate such that a cutting edge of the dozing blade penetrates downward and forward through the material of the substrate, overcoming the structural integrity of the material, and causing it to fail. In large scale surface mining activities, a tractor, typically equipped with ground engaging tracks, may make successive passes across an area where surface material is to be removed, forming a slot in the substrate in each pass. Due to the harsh environment, frequent repair, replacement, and servicing of the equipment is often necessary. Moreover, to maximize productivity it is often desirable to employ machine operators who are highly skilled. Operators of lesser skill are often observed to manipulate a dozing blade or otherwise operate a tractor such that the tractor stalls while attempting to form a slot in a substrate. In other instances, rather than stalling the tractor, operators can sometimes cut a slot that is too shallow than what is theoretically possible, or even skim the dozing blade across a surface of the substrate without loosening any substantial amount of material over at least a portion of a given pass. Stalling the machine, or removing too little material, understandably impacts efficiency. For these and other reasons, there remains a premium in the pertinent industries on sophisticated equipment design and operation, as well as operator skill.
U.S. Pat. No. 3,238,648 to D. E. Cobb et al. is directed to a bulldozer with a stinger bit, for the apparent purpose of enabling a reasonably deep cut through hard material without overtaxing the tractor engine and tractive ability. These goals are apparently achieved by making the stinger bit adjustable or retractable, such that it can be used to ease initial penetration. This design would apparently enable a normal use of the full width of the blade, and an alternative use with the stinger bit extended. While Cobb et al. may have provided advantages over the state of the art at that time, there remains ample room for improvement. Moreover, the features necessary to enable the functionality of the stinger bit, such as hydraulic actuators and the like, can add non-trivial expense, complexity and maintenance requirements to the machine.